What are your water parameters?
Ammonia
NitrIte
Nitrate
pH
KH/
GH
TDS
Temperature
Any other measurements, you might have.
How long has the tank been running?
Are you familiar with the nitrification cycle? The article in my signature "Getting Started" can help with over all tank care an explains it also.
As mentioned above, genetics can cause these mutations to be weak. But you might have the ability to maximize your tank environment and hope for them to grow up.
__________________

New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?

Start here - Aquarium Advice Article
https://www.aquariumadvice.com/guide...ater-aquarium/
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves